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StringHash.h
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/*
* Copyright (C) 2006, 2007, 2008, 2012, 2013 Apple Inc. All rights reserved
* Copyright (C) Research In Motion Limited 2009. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*
*/
#ifndef StringHash_h
#define StringHash_h
#include <wtf/text/AtomicString.h>
#include <wtf/HashTraits.h>
#include <wtf/StringHasher.h>
namespace WTF {
inline bool HashTraits<String>::isEmptyValue(const String& value)
{
return value.isNull();
}
// The hash() functions on StringHash and CaseFoldingHash do not support
// null strings. get(), contains(), and add() on HashMap<String,..., StringHash>
// cause a null-pointer dereference when passed null strings.
// FIXME: We should really figure out a way to put the computeHash function that's
// currently a member function of StringImpl into this file so we can be a little
// closer to having all the nearly-identical hash functions in one place.
struct StringHash {
static unsigned hash(StringImpl* key) { return key->hash(); }
static inline bool equal(const StringImpl* a, const StringImpl* b)
{
return equalNonNull(a, b);
}
static unsigned hash(const RefPtr<StringImpl>& key) { return key->hash(); }
static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
{
return equal(a.get(), b.get());
}
static bool equal(const RefPtr<StringImpl>& a, const StringImpl* b)
{
return equal(a.get(), b);
}
static bool equal(const StringImpl* a, const RefPtr<StringImpl>& b)
{
return equal(a, b.get());
}
static unsigned hash(const String& key) { return key.impl()->hash(); }
static bool equal(const String& a, const String& b)
{
return equal(a.impl(), b.impl());
}
static const bool safeToCompareToEmptyOrDeleted = false;
};
class CaseFoldingHash {
public:
template<typename T> static inline UChar foldCase(T character)
{
if (std::is_same<T, LChar>::value)
return StringImpl::latin1CaseFoldTable[character];
return u_foldCase(character, U_FOLD_CASE_DEFAULT);
}
static unsigned hash(const UChar* data, unsigned length)
{
return StringHasher::computeHashAndMaskTop8Bits<UChar, foldCase<UChar>>(data, length);
}
static unsigned hash(StringImpl& string)
{
if (string.is8Bit())
return hash(string.characters8(), string.length());
return hash(string.characters16(), string.length());
}
static unsigned hash(StringImpl* string)
{
ASSERT(string);
return hash(*string);
}
static unsigned hash(const LChar* data, unsigned length)
{
return StringHasher::computeHashAndMaskTop8Bits<LChar, foldCase<LChar>>(data, length);
}
static inline unsigned hash(const char* data, unsigned length)
{
return CaseFoldingHash::hash(reinterpret_cast<const LChar*>(data), length);
}
static inline bool equal(const StringImpl* a, const StringImpl* b)
{
return equalIgnoringCaseNonNull(a, b);
}
static unsigned hash(const RefPtr<StringImpl>& key)
{
return hash(*key);
}
static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)
{
return equal(a.get(), b.get());
}
static unsigned hash(const String& key)
{
return hash(key.impl());
}
static unsigned hash(const AtomicString& key)
{
return hash(key.impl());
}
static bool equal(const String& a, const String& b)
{
return equal(a.impl(), b.impl());
}
static bool equal(const AtomicString& a, const AtomicString& b)
{
// FIXME: Is the "a == b" here a helpful optimization?
// It makes all cases where the strings are not identical slightly slower.
return a == b || equal(a.impl(), b.impl());
}
static const bool safeToCompareToEmptyOrDeleted = false;
};
// This hash can be used in cases where the key is a hash of a string, but we don't
// want to store the string. It's not really specific to string hashing, but all our
// current uses of it are for strings.
struct AlreadyHashed : IntHash<unsigned> {
static unsigned hash(unsigned key) { return key; }
// To use a hash value as a key for a hash table, we need to eliminate the
// "deleted" value, which is negative one. That could be done by changing
// the string hash function to never generate negative one, but this works
// and is still relatively efficient.
static unsigned avoidDeletedValue(unsigned hash)
{
ASSERT(hash);
unsigned newHash = hash | (!(hash + 1) << 31);
ASSERT(newHash);
ASSERT(newHash != 0xFFFFFFFF);
return newHash;
}
};
}
using WTF::AlreadyHashed;
using WTF::CaseFoldingHash;
using WTF::StringHash;
#endif